Short wave communication system



P 1938- N. E. LINDENBLAVD 2,131,108

SHORT WAVE COMMUNICATION SYSTEM Filed April 28, 1936 7 Sheets-Sheet 1l/N/NG AN TRANS m zzm cs M/7'7'ER MAfCH/NG many/7 TRANS- MITTER 2 0TEAMS/\e INVENTOR.

ATTORNEY.

QNILS. E. LINDENBLAD P 1938- N. E; LINDENBLAD 2,131,103

SHORT WAVE COMMUNICATION SYSTEM Filed April 28,1936 7 Sheets-Sheet 2 3ATTORNEY.

Sept. 27, 1938. N. E. LINDENBLAD SHORT WAVE COMMUNICATION SYSTEM 7Sheets-Sheet 3 Filed April 28, 1936 INVENTOR. NILS E. LINDENBLAD Ag/k/x. A 1w 9 IRA/VS- MINER ATTORNEY.

Sept. 27, 1938 N. E. LINDENBLAD SHORT WAVE COMMUNICATION SYSTEM 7Sheets-Sheet 4 Filed April 28, 1936 D R Y OM E m m E O V W W NL .42 QZ'VA A A 1 A s L MM 4 0 g. 2 3, 3 M L Q 4 4 f 7- 42 F. +4.. Y p w B 3 Wm42 a] 4 T o 7C L 7. 2 U 7 Q1 Q a v e L m W "M 42 J52 a \mms LI MAME kmmmm -42 MM A L 7'0 TRANS 0R RECEIVER Sept. 27, 1938. N. E. LINDENBLAD2,131,108

SHORT WAVE COMMUNICATION "S1ISTEM Filed April 28, 1936 7Sheets-Sheet 5INVENTOR. NILS E. LINDENBLAD BY H? firm ATTORNEY.

Sept. 27, 1938. N. E. LINDENBLAD SHORT WAVE COMMUNICATION SYSTEM FiledApril 28, 1936 7 Sheets-Sheet 6 INVENTOR. gNILS E. LINDENBLAD ROOF PM TEATTORNEY.

Sept. 27, 1938. N. E. LINDENBLAD 2,131,108

SHORT WAVE COMMUNICATION SYSTEM Filed April 28, 1936 7 Sheets-Sheet 7 70ANTfA/A/A (H610) "j FILTER {53 EA 4 1 l i I 70 W050 l 4 1 TRANS. I

VOICE }m4/vs. 54 2 INVENTOR.

' NILS E. LINDENBLAD BY m ATTORNEY.

Patented Sept. 27, 1938 PATENT OFFICE SHORT WAVE COMlIUNICAT-ION SYSTEMNils E. Lindenblad, Port Jefferson, N. Y., assignor. to RadioCorporation of America, a. corporation of Delaware Application April 28,193 6, Serial No. 76,745

Claims.

This invention relates to improvements in antenna systems and to theassociated equipment for use therein.

Some of the objects of the invention are; to

5 obtain substantially uniform radiation in the plane of the radiatingelements; to enable the transmission of waves substantially uniformly inthe horizontal plane; to provide an antenna which has a substantiallyuniform response charl acteristic over a wide band of frequencies,- suchas might be used for television: to provide a rigid and practicalantenna'structure for use on the tops of high buildings wherein thefeeders themselves form supports for the radiating elements; to matchthe surge impedances of the radiating elements to the impedances of thesupporting feeders; to obtain an impedance match between a plurality ofbranch feeders and a main feeder without introducing excessivecirculatingenergy in the system; to. provide an impedance matchingdevice in'the form of a concentric transmission line; to enable theconnection and impedance matching of a single concentric conductorsystem to a plurality of concentric conductor systems.

The invention includes among its features:

(1) An antenna system having a plurality of aerial or radiatingconductors angularly disposed at substantially 60 with respect to eachother, located in the same plane, and so arranged and energized as toproduce substantially uniform radiation in the plane of the elements.

(2) An antenna unit having three aerial or radiating elements which formsides of an equilateral triangle, each of whose sides is equal toonehalf the length of the communication wave, for effecting uniformradiation in the'plane of the unit.

(3) An antenna system formed of a plurality of units in differentparallel planes, each unit of which comprises an equilateral triangularaffair having a plurality of half wavelength conductors which areangularly disposed at substantially 60 with respect to one another, theconductors in one unit being fed at points intermediate the ends whilethe conductors in a parallel plane are fed from the ends.

(4) A feeder in the form of a concentric line having inner and outerconductors whose relative diametrical dimensions vary to produce desiredchanges in impedance of the feeder.

(5) An arrangement for feeding an antenna system directly from the sameelements which support the aerial or radiating conductors.

(6) A metallic bracing structure for the supporting feeders, whichmerely acts as an inductance shunted across the aerial elements.

Among the advantages obtained by the present invention is the provisionof a novel type of impedance matching circuit which is compact, me- 5chanically rigid, and electrically self-shielding.

Other objects, features and advantages will appear from a reading of thefollowing description, which is accompanied by drawings wherein likereference numerals indicate like parts throughout the figures. 2

Figs. 1, 1a and 2 illustrate simplified antenna systems in accordancewith the invention, for obtaining substantially uniform radiation in theplane of the aerial elements;

Fig. lb is an approximate radiation field pattern in the plane of theaerial elements for a sys-' tem such as is illustrated in Figs. 1 andla;

Figs. 3, 4, 5, 6, 6a and 7 illustrate various antenna embodiments of'theinvention employing aerial elements which form sides of one or moreequilateral triangles;

Figs. 4a, 4b, 7a and 7b are given for the purpose of exposition and showthe current distribution pattern in the aerial elements of adjacenttriangular units; I

Fig. 7c is a view showing the system of Fig. 'l unfolded in a singleplane in order to more completely illustrate the structure of Fig. 7 andthe manner in which the various elements thereof are energized;

Figs. 8, 9 and 9a show different metallic brace arrangements across thefeeders for providing greater mechanical rigidity of the antennastructure;

Fig. 10 illustrates a preferred embodiment of antenna, impedancematching system, and feeder system in accordance with the invention;

Fig. 11 is a detail of the system of Fig. 10 showing one pair ofsupporting feeders and associated apparatus in order to more clearlyillustrate the principles of the invention;

Fig. 110. discloses an alternative arrangement to that of Fig. 11 forfeeding the doublets of the diiferent triangular units;

Fig. 12 illustrates a circuit arrangement of filter and impedancecircuit which may be employed infeeding energy from a plurality oftransmitters to. an antenna system of the type shown in Fig. 10.

Fig. 1 shows a simplified antenna system for practicing the presentinvention comprising a pair of V-shaped aerial wires 1, 2 angularlydisposed at substantially 60 with respect to each other and located in asingle plane, such as the 55 mediate their ends, instead of at one oftheir ends, and one way of "accomplishing this is shown in Fig. 1a,wherein each doublet is fed from a 'separate transmission line 5' whichconnects with the antennatuning and. impedance matching circuit 4. Inall other respects the systems of Figs. 1 and 1a are similar.

An essential condition in the practice of the invention is that thecenters of the angularly disposed doublets should not physicallycoincide in the plane of the wires, or, putting it another way, thebranches should not make the symmetrical configuration of an X, althoughthe more closely adjacent ends of the doublets may cross one another tosome extent. In the last case, where the doublets do cross each other tofrom the doublets of the V are in phase in certain directions, such asin the plane of the bisector which is perpendicular to the plane of theV wires, in which directions the centers of the doublets are on the samewave front and have no space difference, whereas in other directionssuch as along a line passing through the centers of the branches of theV, the radiations from the doublets of the V are in opposing phase butdisplaced in space to prevent cancellation of the radiations from thetwo doublets of the V. In the last particular instance the idealarrangement would be to have a space displacement between the centers ofthe branches of the V equal to half the length of the communication waveor an odd multiple thereof. Such spacing, however, is detrimental touniform radiation in the plane of the V because there are two factors tobe considered; namely, maximum radiation efiiciency and minimumvariation in the radiation pattern in the plane of the wires. These twofactors depend to an extent upon the linear spacing between the doubletsof the V while maintaining the angle between the doublets approximatelyconstant. If the linear spacing between centers of the doublets of the vis greater than, let us say, one-half wavelength-then for certain ofthese spacings beyond one-half wavelength there is obtained maximumradiation in directions other than the plane of the wires. Consequentlythere are certain spacings between the centers of the branches whereinthere is a compromise between maximum radiation emciency of the systemand minimum variation in the a spacing of approximately one-quarterwave, from which it will be seen that radiation is substantially uniformin the plane.

The radiation pattern of a single V in accordance with the invention isconsiderably improved by adding a third half wavelength doublet betweenthe morewidely spaced ends of the V to provide an antenna system in theform of an equilateral triangle, each angle of which is 60. One sucharrangement is shown in Fig. 3, wherein each doublet or radiatingelement 5", 6 or 1 forms with each adjacent doublet a V, thus eachdoublet is a side of two .V's. In the system of Fig. 3, the spacingsbetween the centers of all doublets are such as again to provide minimumvariation of the radiation pattern in the plane of the wires. Theoptimum value of spacing for maximum uniform radiation in the plane ofthe triangle can be determined by trial, since the mathematicalcomputations involved are exceedingly complicated. By experiment,spacings have been found where the variation is substantially not morethan 5% in amplitude. Such order of uniformity of radiation has beenobtained with spacings between centers of the wires of an equilateraltriangle, such as herein described, of approximately a quarter of thelength of the communication wave, or half the length of each side of thetriangle, although it is to be distinctly understood that the inventionis not limited to this particular spacing.

Doublets 5", 6 and 1 are coupled together by half wavelengthradiationless loops A, B and C and energized from high frequencytransmitter 3 connected to one of these loops, here shown as C throughtransmission line TL. This line connects with loop C at points where theimpedance of the line is matched to the impedance of the loop andantenna. The lengths of the loops A, B and C are so chosen as to givedesired opposite instantaneous polarities on adjacent ends of adjacentdoublets as indicated. If desired, the system of Fig. 3 can be fed inother ways; for example, each doublet 5", 6, I can be energized atpoints intermediate their ends in the manner shown in Fig. 1a, in whichcase loops A, B and C will be dispensed with.

Fig. 3 is merely one unit which gives uniform radiation in the plane ofthe triangle, and to obtain greater directivity in a plane perpendicularto the plane of the triangle, several such units may be stacked oneabove the other. Fig. 4 shows, by way of example, one embodiment bymeans of which this stacking can be achieved.

In Fig. 4 there are shown four horizontal equilateral triangular unitsD, E, F and G stacked one above the other and spaced one-half wavelengthapart. These equilateral triangular units each comprise half wavelengthdoublets which are energized through vertical supporting feeder lines 8,9 and ill, in turn, connected to line TL and transmitting apparatus 3.The triangular units are so arranged that correspondingly located wiresin the different units connect with the lines 8, 9 and ill to producesimilar voltage curves therein. These voltage curves are indicated bybroken lines on all the doublets of the units, as well as theinstantaneous -polarities at the ends of the doublets. The optimum valueof the spacing between doublets of an individual triangular unit, 1. e.,the spacing which gives a minimum of variation in radiation at goodradiation efliciency, where several triangular units are made to form anantenna array will now vary from the simple case of Fig. 3, and shouldagain be determined by trial, because of the mu-f tual reaction betweenthe triangular units. The vertical broken line of sine wave formindicates the standing wave on each vertical. feeder of a pair. Sinceadjacent feeders of'the; same pairs each have standing waves of oppositeinstantaneous polarity at correspondingly'located points along thefeeders, there will be radiation cancellation. The feeders of eachpairarejsepa- S. The transmission line TL from the transmitter 3 ismatched at the bottom of one corner ofone pair of feeders, here shown as8, although it.

The equilateral triangular units D,'-"E, F' and t G, are spaced one-halfwavelength apart, for

which reason, to obtain like polarities in similar- 19 located doubletsof the units, the individual" doublets of adjacent triangular units mustbe connected to opposite sides of the vertical feede x ers. This mode ofconnection of the triangularv 1 units to the feeders appears moreunderstandable from Figs. 4a, 4b which show 'the'individual triangles asthey appear from a plan view. .Aiternate triangles would appear inithesame way.

The feeder pairs 8, 9 and iii are respectively terminated attheir'lowerends by loopsA', B and C each of which has an overall lengthof a half 1 wave, each leg of the loops being aquarter wave-'* length.Consequently, if the loops are made-to be extensions of the feeder pairs8, 9 and i0, as

shown in the drawings, and their midpoints rest, on a support, thetuning of the antenna system will not be afiected by such supports sincethe midpoints of the loops A. B and C" are voltage to the terminalimpedance of the radiating doubletsof the triangular units.

of both the radiating doublets and the feeders.

The feeders of the system, of course, need not be matched to thetriangular units to provide a practical systemfor radiating oneparticular frequency or a narrow band of frequencies such as intelephony. Where, however, a wide band, such as in television, isrequired tobe uniformly radi ated, it is essential that all feeders bematched to the radiating doublets to insure a minimum ratio ofcirculated energy in the system versus radiated energy from the system.The desired matching may be obtained by employing a plurality of stackedtriangle units of the type shown in Fig. 3. Such an arrangement isillustrated in Fig. 5, which shows, as an example, only two triangularunits H and I, and wherein the correspondingly located loops of thetriangular units A", A', B", B' and C", C are connected to the verticalfeeders ll, i2 and i3 at points on the loops where the impedance valueequals the characteristic impedance of the feeder. As the load of eachstacked unit is added to the preceding unit as we move away from thetransmitter 3, it will be observed that the points of capacitors lconnection on. the at. A", a" and c" to the .vertical feeders ll, i2 andit will approachthe radiating doublets of the associated triangularunits I less closely than the points of connection on thecorrespondingly located loops A', B'. and-C"! of the lower or precedingunit H.

Fig-6 shows a; modification of the antenna of theinventior'i, somewhatsimilar to the arranger ment of .4, except for the positioning and ratedat voltage nodal points by suitable spacers Figufithere are shown threeequilateral triangular units K, L and M which ai'espaced onehalfwavelength apart, and. midway between adjacent triangular units on thevertical feeders i4, i5 and [6, there are metallic transverse spacers Sfconductively connecting together each pair of feeders; The points wherethese spacers ooh- I tact thefeedersare voltage nodal points for thestanding waves produced on the'feeders. 1 Cross connections I'I areprovided on .both sides 'of the spacers Sfor' connecting each feeder'ofeach .pair' on one side of the spacer to the other feeder of the samepair on the other side of the spacer :to provide the-equivalent of atransposition of v the feederjwires at the voltage nodal point betweentriangular ,units.

videlmech'anical"advantages for the system: -It

25 The spacers merely prowilifbe observed that similarly locateddoublets of 'all triangular-units K,-L and MQare connected to the samefeeder wires. This. arrangement employing.metallicispacers is, inpractice, not

due mainly. to'th'e introduction of inductancein suitable for useqwhereit is desired to match, the I. characteristic impedanceof. thefeeders tothe terminal impedance of the radiating'doublets, 35 g ductance can betuned out" by further' con'iplieating. heantenna system with?compensating along the feeder pairs. In this figure, just as Fig. 6a isa modification of'Fig. 6, which eliminates the need for transposition.ofthe feeders between radiating units, sincein this case the" triangularunits are spaced one'wavelength apart as high definition television, itis of utxnostflirn portance that the antenna systemuhaveainini mumratio"of circulating energy-in thejsystem to radiated energ'yfrom thesystem,=i. e., 'ahigh. power factor. The systems of Figs; 7,10,.11 and12, to be described hereinafter, have-been found;

to be especially suitable and superior .for. this purpose to any ofthe'systems beforedescribed. To achieve this desirable result, theindividuailkdoublets of. the triangularunits of. Figs. 7,10, '11 and 12are connected to the feeders at such points on the radiators where theimpedance of; the rai diators match the: characteristic. impedance;of'-I the feeders.

antenna tuning and impedance matching device Fig.7 shows onesatisfactory. antenna embodic 1 ment for achievingwide1-frequency"band,come,

munication. Here there are provided'six transf, mission linescomprisingthree pairsof vertical feeders i8,,l9;*;20,;2l and 22, 23,each of'which connectswith a' two-wire transmission. line extending tohigh frequency apparatus through.

ation even when the spacing is an appreciable fraction of a wavelength,for example an eighth of a wavelength. The fact that these feeders canbe separated without producing radiation is utilized in making the cageserve as a support for the triangular radiating units N, O and P. Eachunit comprises three half-wavelength doublets forming sides of an openequilateral triangle.

'Unit P contains doublets 24, 25 and 26; unit 0 contains doublets 21, 28and 29; and unit N contains doublets 30, 3| and 32.. The feeders l8, I9,20 etc. are in the form of rigid pipes on which the individual doubletsof the equilateral triangular units may be mounted directly or, as shownin the drawings for mechanical and electrical reasons, supported throughmetallic brackets 25. All brackets 25' are of the same length and theimpedance of these including the vertical feeders are matched to theimpedance of the doublets at spaced points on the doublets intermediatethe ends thereof in well known manner. In other words, each doublet isarranged to introduce a load which matches the vertical feeders at thepoints of connection so that a minimum or no standing wave is set up onthe vertical feeders. Since the phase lag introduced by the additionallength of brackets 25 is the same in all triangular unitsN, O and P,they do not affect the phase relations between the triangular units. Theunits are here shown spaced one-half wavelength apart, correspondinglylocated doublets of which are located one wavelength apart. Sinceadjacent equilateral triangular units are one-half wavelength apart, thesame feeder will have opposite polarities at the points of connection sospaced, for which reason it is necessary to reverse the order ofpolarity connection of the individual doublets of the adjacenttriangular units so that the currents in adjacent triangles may have thesame direction. This current direction is illustrated in Figs. 7a and 7bas being counterclockwise, although it will be appreciated that thedirection of the currents in all the equilateral triangular units N, Oand P may be reversed. Figs. 7a and 7b are plan views of the triangularunits P and 0, respectively, and indi- 'cate how the individual doubletsof each unit on each level are fed from different feeder wires. It willbe observed, among other things, that the doublets of adjacenttriangular units, such as P and O, are differently positioned, whilethose of alternately located units, such as P and N, are similarlypositioned. Referring to Fig. 7a as an example, it will be seen thatfeeders i8 and 23 feed doublet 24 of unit P, whereas in the adjacentlower unit 0, (note Fig. 7b) these two feeders help feed two differentdoublets. The manner of feeding all doublets of the triangular units N,O and P will be more clearly understood from an inspection of Fig. 70,which is an unfolded view of the antenna structure as it would look ifthe feeders and doublets were all placed in a single plane.

When feeding the system of Fig. 7, as shown in 7c, it may be desirableto change the dimensions of the feeders I8, i9, 20 etc. abruptly atsuccessive levels at which they connect with the different triangularunits. because of the abrupt change in load impedance on the feeders asthe feeders extend past a level of a triangular unit and approach thetop of the antenna. In Fig. 7

- the diameters of the feeders decrease toward the top of the antennasystem, as shown, with a consequent increase in impedance, of thefeeders. In practice, it is difficult to obtain a complete a,1s1,1'oe

impedance matching of the feeders throughout their lengths since thiswould call for large changes in diameter of the feeders. A slightmismatch of the feeders, especially if the voltage nodal points of thethus created standing wave portion of the total energy on the feeder(since some standing waves are created with a mismatch) are locatedmid-way between adjacent triangular units, is not, however, detrimentalto the system, since in this condition the polarities at the terminalsof each half wave section between adjacent triangular units is reversedand of equal amplitude regardless of whether there is a standing ortraveling wave in the section.

If now we consider a case where the maximum point of a standing voltagewave on the feeders instead of a minimum falls midway between adjacenttriangular radiating units, we may have a very different mode of tuning,if at the same time the impedance offered by the individual doubletsacross the feeders is inductive. The case then is similar to thesituation described in my United States Patent No. 1,821,386, grantedSeptember 1, 1931, wherein there is obtained an infinite phase velocityalong the feeders so that all points along each feeder is at the samephase. In this particular case the adjacent triangular units do not needto have the order of connection of the individual radiating doubletschanged as shown in Figs. 7 to 70, and instead all triangular units mayhave their correspondingly located doublets similarly located along thefeeder line. Because of this phase phenomenon, there is no need toemploy any particular spacing between adjacent units. It is evident thata system built to operate according to the principles above set forth inconnection with Fig. 7 will have this second degree of freedom (ortuning) just described at a lower frequency. The entire feeders andthose portions of the individual radiating doublets in the triangularunits falling outside the tapping points on the doublets are theneffective capacities which are tuned by the portion of theradiating'doublets between the tapping which are effective inductances.of oscillation, however, is not preferred since it calls for a greaterratio of circulating energy in the system to radiated energy from thesystem which tends to give the system a lower power factor andconsequently sharper tuning, a feature not desirable in connection withcommunication on wide frequency band high definition television signals.

Fig. 8 is a modification of Fig. 7 and for purposes of simplicity merelyshows the uppermost triangular unit, since the remainder of the systemis indentical with that of Fig. 7. In this new figure there areprovided, for the sake of mechanical rigidity, U-shaped metallic braces26 which fit into or are attached in suitable manner to the upper endsof the vertical feeders. Braces 26 act merely as inductances shuntedacross the portion between the tapping points on the doublets. Thus thetotal inductance of each doublet is decreased, from which it followsthat the natural period of the doublet increases. It should be observedat this time that since adjacent feeders are of opposite phasethroughout the cage of feeders, it does not matter electrically whetherthe braces are connected across the pairs of feed- This last mode iii)team, it will be noted, takes the form of a six which feed a singledoublet. From a mechanical standpoint, however, it is more advantageousto connect the braces across feeders of different pairs than acrossfeeders of the same pairs.

between pairs of feeders. This new bracing syspoint star. Fig. 9illustrates a plan view of such system, as illustrated in connectionwith Fig. 10, is used for each triangular unit of doublets. The bracesof Fig. 9 comprise straight metallic straps or bars 2! which arefastened to each other at their points of intersection in suitablemanner, such as by welding, soldering, riveting, bolting, threading,etc. Where size permits, the whole brace may be a single casting, orsectionalized into small castings; in the latter case the castings willbe fastened together.

Electrically the only portions of the six star brace of Fig. 9 whichcarry current and act as inductances are those which form, the contouror outline of the star. This is more clearly illustrated in Fig. 9awhich shows in unbroken lines the electrically active portions of thestar, while the broken lines indicate the electrically inactiveportions. The points of intersection of the portions of the bracearrangement are intermediate the points of opposite polarity on thevertical feeders and consequently are of zero potential, as indicated.The members of the bracing system represented by the broken lines arethus connected betweeen points of zero potential and therefore carry nocurrent except secondary currents by induction. Such a bracingarrangement as shown in Figs. 9 and 9a, in combination with the verticalfeeder columns, forms an excellent mechanical structure resembling aself supporting tower. If desired, one or more feeder lines can be runthrough the zero regions of the braces along the length of the structureand supported thereat for other systems, such as antennas, weatherobservation instruments, or other arrangements which it may be desiredto mount at the top of the antenna system of the invention.

It should be noted that the systems of the figures hereinabovediscussed, which show a plurality of triangular units stacked inparallel planes, in accordance with the invention, such as Figs. 5, 6,6a. and 7, have been energized from the base of the antenna structure.From what has been said before in connection with. these figures, itwill be apparent that due to the half along the length of the feederswhich occurs in the presence of sidebands due to the deviation of thesideband wavelengths from the particular wavelength for which thetriangular units are I correctly spaced. Thus while the tuningcharacteristic of each triangular unit of the system of Figs. 5, 6, 6aand 7 may be sufficiently broad to just referred to.

accommodate the sidebands without appreciable change in amplitude in theradiating elements, the cumulative effect mentioned will disturb, tosome extent, the radiation pattern and, therefore, at the distant pointof reception cause an apparent greater change in received amplitude thanthat which is actually caused by the tuning characteristic of thetriangular units.

The system of Fig. 10, now to be discussed in connection with Fig. 11,shows one preferred embodiment in accordance with the invention andovercomes, to a large extent, the foregoing disadvantage by minimizingthe cumulative error This is achieved, in brief, by connecting only thecenter triangular unit R. directly to the source of energy by means offeeder lines and coupling the other triangular units W and Q,respectively above and below the center unit, to this center unit R. Forthis purpose there are employed sections of concentric transmissionlines 30 to 35 respectively, whose inner conductors are directlyconnected to the doublets of the center triangular unit and whose outerconductors serve as coupling feeders for the doublets of the lowertriangular unit Q, there being provided an extension 35 of the outerconductor for serving as a coupling feeder for the uppermost triangularunit W. These self-contained concentric transmission line feedersprovide, among otherthings, a clean mechanical design of structure.

Fig. 10 shows three equilateral triangular units 'Q, R and W in parallelplanes at different levels, spaced one-half wavelength apart, and fed bythree pairs of vertical feeders. In order to more clearly explain themanner in which the doublets of Fig. 10 are fed by and matched to thevertical feeder lines, Fig. 11 shows, in simplified manner, a singlepair 3| 32 of the feeders if Fig. 10 with the associated doublets of thedifferent triangular units connected to this pair. Since the other pairsof feeders, namely 33 to 35, are connected in similar manner to theother doublets of the likewise applies to these other feeders and theirassociated doublets.

The middle doublets 31, 31' which are the ones primarily receivingenergy from the inner conductors 38 of the transmission lines 3|, 32*areat their ends 56 connected to feeders 58 running more or less parallelwiththe doublets 31, 31'. These feeders 58 connect the ends 56 of thedoublets to the ends 59 of the inner conductors 38 of the concentriclines 3|, 32. These ends 59, as described later, have an impedance whichis rather high, for which reason it is advantageous to make the lastquarter wavelength of the inner conductor 38 of the concentric line havea higher ratio between diameters of inner and outer conductors than therest of the system. As is known,

triangular units, what is set forth hereinafter it is the diametricalratio and not the actual tained at the feed points 59 will now begiven.' In considering a single doublet 31, we know that its seriesresistance at its center, is '72 ohms. If

we now consider two doublets directly connected in parallel, closetogether and connected to each other at the ends, we know that they aresur- 'of them must then be four times that of a single doublet alone,for the same power. If the division of the current between the twodoublets effectively in parallel is not equal, the series resistance atthe middle of one is equal to 72 ohms multiplied by the square of theratio of the total current in the system and that in the branch underconsideration. Now, as a matter of fact 4 the inner conductors 88 of thetwo transmission lines ii, 32 are connected to the feeders 58 not at themiddle of the system but at points farther out (although symmetrical).Due to the falling oil! of the current towards the ends of a doublet, itcan-be seen that, on an energy basis, the series resistance of thesystem is still further increased.

The actual length of the feeders 58 between the ends of the doublets andthe ends of the inner conductors 38 of the transmission lines is lessthan a quarter wave. In the concentric transmission lines, however, thecenter conductor current must have an equal and opposite counterpart inthe outer conductor, which is called the shell current. This shellcurrent in the outer conductor continues through the aperture in theouter conductor made for the end of the center conductor and continuesacross the mid portion of the system (star connection and center portionof main doublet) to enter in through the aperture of the othertransmission line to again become the shell current. The star membersand the portion of the main doublet intermediate two adjacenttransmission lines feeding the same doublet serve to complete the pathfor the split doublet branch formed by the feeder. The current from thefeeder branch, however, causes a certain voltage drop across the starmembers and the middle doublets which is not obtained in thetop andbottom systems. This is equivalent to making the inductance of the midportion of the mid system higher. The length of the doublets in the midsystem therefore has to be somewhat less than in the top and bottomsystems. The total voltage drop obtained across the mid section (starsand mid portions of the doublets) is, of course, what energizes the topand bottom systems.

In actual practice, due to the shunting effect of the bracing .starconnections, the doublets of all the units W, R and Q are very slightlylonger physically than one-half wave, the doublets of the middle unit. Bbeing slightly shorter physically than the doublets of units W and Q. Inone em-' bodiment, the upper and lower -doublets were about 4% longerthan the physical length of onehalf wave, whereas the middle doubletswere only about 2% longer than one-half wave, although it will beunderstood that the electrical length of all the doublets of Q, R and Wis a perfect half wave. This difference between the middle doublets andthe upper and lower doublets is due to the connections of the feeders 58to the ends J of the middle doublets.

From the foregoing it will be appreciated that it is not essential thatfeeders ll be connected only to the ends 55 of the middle doublets,since they may be tapped to the middle doublets at intermediate pointsdepending upon the' impedance matching requirements of the system.

Such impedance matching requirements, under certain conditions, may evencall for the introduction of lumped feeders 58. e

For obtaininga 180 phase reversal between the adjacent concentrictransmission lines ii and 32, there is provided a U-shaped concentricline section 39 so connected to an energy supply line 40 that there is apath difference between lines fl and 32 equal to half a wave as measuredfrom the point of connection 4|. In other words, the path to onetransmission line 42 is half a wave longer from junction point 4| thanto the other transmission line II, and both paths are in parallelrelation with respect to energy line 40. Other U-shaped concentric linesections 42 and 43 similarly couple the other concentric transmissionlines 30, 35 and, 34 together, and are, in turn,

connected to energy supply feeders 44 and 45. This mode of coupling isadequately described in copending application Serial No. 634,000, filedSeptember 20, 1932, by Albert Gothe et al.- to which reference is madefor a more detailed description. It will thus be seen that the sixvertical concentric transmission lines to 35, inclusive, of alternatephase, have been reduced to three energy supply feeders 40, 44 and 45 ofthe same phase. To obtain the desired impedance matching between theU-shaped line sections 39, 42 and 43 and their respective energy supplyfeeders 40, 44 and 45, the impedance of each feeder 40, 44 and 45 isrespectively made to be equal to one-half the impedance of the U-shapedline reactances in some form in section which it will be observedcomprises two I transmission lines in parallel. For example, if theimpedance of each transmission line of the U-shaped section 38 is 48ohms, then the impedance of energy feeder should be 24 ohms for aconnection which is free from reflection. The

surge impedance of the U branches therefore must be twice that of the Tbranch feeding into the U. Since the surge impedance of a line is equalto center conductor diameters, is under a logarithm.

That then means that if L is to be doubled or C out in half, the ratioof diameters must be squared. If L was to be made three times and C tobe divided by three the ratio would have to be cubed. It can be seenfrom this that line dimensions must be carefully chosen in order thatimpossible mechanical dimensions be avoided.

It is now proposed to connect all three feeders.

40,44 and of 24 ohms each to a single feeder.

At first blush, one might consider simply par-,

alleling the three feeders. However, if this is done, then for aconnection free from reflection with a single feeder for energizing thethree, there would be required a single feeder whose impedance is equalto that of the three feeders 40, 44 and 45 in parallel, that is, asingle feeder whose surge impedance is only 8 ohms. Such a practical inthis case inasmuch as a desirable ratio of four to one between inner andouter conductors of a concentric line gives a surge im pedance of about80 ohms, and in order to obtain an impedance of only eight ohms to matchthe three parallel lines 40, 44 and 45 there would be required a ratiobetween inner and outer conductors of the single feeder of the tenthroot of four, an obviously impractical mechanical arrangement becausethe inner and outer conductors would then have an extremely smalldifference in diameter.

The foregoing difllculties are overcome in accordance with the inventionby arranging a circuit whereby the three T feeders 40, 44 and 45 areconnected in series and joined to-the single feeder 46. By means of thisfeature of the present invention, the impedance required for the singlefeeder 46 is three times that of one of the feeders '48, 44 or 45, inother words 72 ohms. This ohmage is a practical amount which the mainline or single feeder 46 can be designed to provide. As can be seen, twoof three T branches 40 and 44 are surrounded by a shell 41 which makesthe outer conductor of the T branch an intermediate shell 48 for thelength of a quarter wave. On account of its length, this intermediateshell 48 has a very high impedance on its outside. Now, then, thecurrent in the center conductor 49 of the branch 45, which has no outershell,'becomes the shell current for the middle branch 44 and thecurrent of the center conductor 50 of the middle branch 44 becomes theshell current for the branch 40. The current in 49 cannot go on theoutside of the intermediate sleeve 48 of the middle branch 44 due to thehigh impedance of a quarter wave conductor; but must go on the insideand become the shell current for the middle T branch 44 as alreadystated. The shell current of the branch 45, i. e., the current in theouter conductors, follows the cover 5| and becomes the shell current forthe main line 46. The center conductor current of the right hand branchbecomes the center conductor current of the main line. The three Tbranches arethus connected in series and in phase with the main line 46.Due to the necessary introduction of cross connectors 52 in this system,it is rather important to make the three T branches 40, 44 and 45successively longer by an equal amount. Since the voltage of the mainline 46 is divided by three, a third for each T branch, or since thereare three T branches in series, the surge impedance of each branch mustbe-a third of the surge impedance of the main line 46. The

ratio of the shell and center conductor diameters of the T branches 40,44 and 45 must therefore be the cubic root of the ratio in the main line46 as already stated.

Fig. 11a shows an alternative method to that of Figs. 10 and 11 ofconnecting a pair of concentric transmission lines, such as 3|, 32, tothe doublets of three triangular units, and difi'ers from Fig. 11 onlyin showing that the concentric lines 3|, 32 may both feed the samedoublet in the middle level, instead of different doublets. whilefeeding different doublets in the upper and lower levels. I

Where it is desired to employ two transmitters on the same antennasystem at slightly different frequencies, (M and M) as for instance thevideo and audio transmitters for transmitting television programs, afilter'system shown in Fig. 12 may be inserted betweenthe main line 46of Fig. 10 and the transmitters proper. This filter system, shown in boxform and designated 58, is described in great detail in the copendingapplication of Philip S. Carter, Serial No. 88,073, flied June 30, 1936,to which reference is herein made.

Obviously the purpose of this filter system is to prevent the energyfrom one transmitter from enterins the circuits of the othertransmitters while P rmitting both transmitters to freely feed energyinto the antenna system.

Since main feeder 46 is a single concentric line and since thetransmitters in the above mentioned case of Fig. 12 are preferably ofthe push-pull type it now becomes necessary to adapt the singleconcentric transmission line system to a push-pull transmission linesystem for connecting to the balanced circuit of the transmitter. Inthis instance, the U-shaped phase transformmg arrangement describedabove in connection with elements 39, 42 and 43 of Fig. 10 was not foundsuitable for providing the proper load impedance required by thepush-pull transmitter. This will be evident from the fact that the mainline 46 has an impedance of 72 ohms and the total impedance across bothlegs of a U-phase transforming arrangement would have to be 288 ohms, i.e., each leg of the U would have an impedance of 144 ohms. Such animpedance of 288 ohms is for most transmitters too high to draw fullpower. This difficulty is overcome in accordance with another aspect ofthe invention which provides a push-pull impedance equal to theimpedance of the single concentric conductor line which again effectsphase transformation. This circuit comprises a quarter wave concentricline 6| whose inner and outer conductors are each connected at one end62 to the center conductors- 63 and 64 of a pair of push-pull concentricline branches. An outer metallic sleeve 66 surrounds the line 6| for itsentire quarter wavelength, and is joined to the outer conductors of thepush-pull branches, as shown. To understand the operation of thecircuit. let us visualize the circuit from the transmitter and fromwhich there are fed currents'of opposite direction in the two pushpullbranches, as indicated by the arrow marks. Since in a single concentricconductor line the center conductor current and the shell current on theinner surface of the outer conductor are opposite to each other indirection, but of the same magnitude, it follows that the innerconductor of one branch of the push-pull circuit should continue astheinner conductor of the single concentric line 6| while the innerconductor of the other push-pull branch should con tinue as the shellcurrent of the line 6|. To prevent short circuiting of the push-pullbranch connected to the outer conductor of line 6|, it is necessary forthe shell of line 6| at point 62 to present a high impedanceon its outersurface, in which case all current arriving over conductor 64 willtravel over the inner surface of the shell of line 6|. This is achievedby making sleeve 66 a quarter wavelength and connecting its upper end tothe outer conductorof line 6|. Since lines 63 and 64 are effectively inseries, each must have a surge impedance equal to half thesurgeimpedance of the line 6|; consequently, there will be a surge impedanceacross 63 and 64 of a value equal to the surge impedance of singleconcentricline6l.

In order not to alter the physical configuration of not to change thesurge impedance along the tapered section, the diametrical ratio of theconductors in this section should be constant. To

preserve neatness of appearance, the metallic,-

sleeve 66 is extended beyond quarter wave line 6| to form a continuationof the transmission line leading from filter 53.

It will be understood, of course, from what has gone before, that theinvention is not limited to the precise arrangements illustrated anddescribed, since various modiilcations may be made without departingfrom the spirit and scope of the invention. a.

What is claimed is:

1. An'antenna system comprising two conductors in the same plane anddisposedsubstantially at an angle of 60 with respect to each other, eachof said conductors being one-half the length of the communication wave,and means for excitin said conductors to have opposite instantaneouspolarities at correspondingly located points.

2. An antenna system comprising two conductors in the same plane and.disposed substantially at an angle of 60 with respect'to each other,each of said conductors being one-half the length of the communicationwave, and a source of high frequency energy for energizing saidconductors to have opposite instantaneous polarities at correspondinglylocated points, whereby substantially uniform radiation is obtained inthe plane of said conductors.

3. An antenna system comprising two conductors in the same plane anddisposed substantially at an angle of 60 with respect to each other,each of said conductors being one-half the length of the communicationwave, and a source of high frequency energy for energizing saidconductors to have opposite instantaneous polarities at correspondinglylocated points, whereby substantially uniform radiation is obtained inthe plane of said conductors, said conductors being fed by said.

source at their more closely adjacent ends.

4. An antenna system comprising two conductors in the same plane anddisposed substantially at an angle of 60 with respect to each other,each of said conductors being one-half the length of the communicationwave, and a source of high frequency energy for energizing saidconductors to have opposite instantaneous polarities at correspondinglylocated points, whereby substantially uniform radiation is obtained inthe plane of said conductors, said conductors being fed by said sourcethrough feeders at points on said conductors which are symmetricallylocated with respect to the centers thereof and so spaced that the impedance of said conductors matches the impedance of said feeders.

5. An antenna system comprising two conductors in the same plane anddisposed substantially at an angle of 60 with respect to each other,each of said conductors being one-half the length of the communicationwave, and a source of high frequency energy for energizing saidconductors to have opposite instantaneous polarities at correspondinglylocated points, whereby substantial ly uniform radiation is obtained inthe plane of said conductors, said conductors being fed by said sourceat their more closely adjacent ends,

to the correspondingly located ends of the eleopen-ended equilateraltriangle, each of said eleing a length equal to one-half the length ofthe communication wave, and means for exciting said elements such thatadjacent ends of the elements have opposite instantaneous polarities.

'7. An antenna system comprising three spaced aerial elements in thesame plane forming an equilateral triangle, each of said elements havinga length equal to one-half the length of the communication wave,connections equal to an odd multiple including unity of half theoperating wavelength connecting together adjacent ends of said elements,and a source of high frequency energy connected to spaced points on oneof said connections for energizing said elements whereby adjacent endshave opposite instantaneous polarities.

8. An antenna system comprising three spaced aerial elements in the sameplaneforming an open-ended equilateral triangle, each of said elementshaving a length equal to one-half the length of the communication wave,another similar equilateral triangle similarly located in a parallelplane, three pairs of feeders connecting the adjacent ends of theelements in one plane elements in the same plane forming an equilateraltriangle, each of 'said elements having a length equal to one-half thelength of the communication wave, a loop having an overall length ofone-half wavelength connecting together the end of one element with theadjacent end of another element, similar loops coupling together theother adjacent ends of said elements, a similar equilateral triangle ofelements in a parallel plane and similarly placed, a pair of feedersconnecting each loop of one triangle with the correspondinglylocatedloop of the other triangle, and high frequency apparatus coupleddirectly to only one of said loops of one of said triangles forenergizing all aerial elements of both" triangles whereby adjacent endsof said aerial elements .in each plane have opposite instantaneouspolarities, similarly located ends of said elements in differentplaneshaving polarities of the same sign.

10. An antenna system comprising three spaced aerial elements in thesame plane forming an ments having a length equal to one-half the lengthof the communication wave, another similar equilateral trianglesimilarly located in a parallel plane, three pairs of feeders connectingthe adjacent ends oi the elements in one plane to the correspondinglylocated ends of the elements in the other plane, said feeders compris-'ing tubular conductors for supporting said aerial elements, said pairsof tubular conductors extending beyond said aerial elements in said lastplane impedance of said connections;

said conductors crossing each other for a portion of their lengths lessthan one-quarter of the length of the communication. wave.

,6. An antenna system comprising three spaced aerial elements in thesame plane forming an equilateral triangle, each of said elements hav11. An antenna system in accordance with claim 10, characterized inthisthat said triangles are spaced apart a distance equal to one wavelength,and the ends of correspondingly located to the same feeders. V

2. An antenna system in accordance with aerial elements in. bothtriangles are connected claim 10, characterized in this that saidtriangles are spaced apart a distance equal to one-half wavelength, andthe ends of correspondingly located aerial elements in both trianglesare connected to the same feeders, said feeders between triangles indifferent planes being transposed.

13. In combination, a plurality of pairs of feeder lines in the form ofsupporting elements arranged symmetrically with respect to a centerpoint, a load connected to each of said pairs and supported thereby,high frequency apparatus coupled to said pairs whereby adjacent feedershave opposite instantaneous polarities thereon, and metallic bracesconnecting the feeders of each pair with the adjacent feeders of theadjacent pairs, said braces being in effect inductances whichelectrically are shunted across said loads.

14. In combination, a plurality of pairs of feeders arranged to form acage, an antenna element coupled to each of said pairs and supportedthereby, high frequency apparatus coupled to said pairs in such mannerthat adjacent feeders have opposite instantaneous polarities, and ametallic brace between adjacent feeders.

15. In combination, three pairs of feeders arranged to form a cage, anantenna element coupled to the feeders of each pair, and a metallicbrace in the form of a six point star mechanically connecting said pairsof feeders together, the points of said star being the location of saidfeeders, the portions of said brace between feeders acting effectivelyas inductances across said feeders.

16. An antenna system comprising a concentric feeder line having innerand outer conductors, an aerial element conductively coupled to saidinner conductor, another aerial element in a plane parallel to the planeof said first element conductively coupled to said outer conductor, saidplanes being spaced a predetermined distance apart, means for supplyingenergy to said inner conductor for directly exciting said first aerialelement.

1'7. A system in accordance with claim 16, characterized in this thatthe planes in which said aerial elements lie are spaced one-halfwavelength apart.

18. An antenna system comprising a pair of concentric feeder lines, eachhaving an inner and an outer conductor, a first doublet having a lengthequal to half the length of the communication wave conductively coupledto said inner conductors, a second doublet of similar length in a planeparallel to the plane of said first doublet conductively coupled to theouter conductor of one of said feeder lines, a third doublet in theplane of said second doublet and conductively coupled to the outerconductor of said other feeder line, and means for energizing said innerconductors of said pair of feeder lines out of phase with respect toeach other, whereby said first doublet is directly excited from saidmeans.

19. A system in accordance with claim 18, characterized in this thatsaid planes are spaced apart an odd multiple of a half wavelength, andsaid first doublet is connected to the ends of said inner conductors.

20. An antenna system comprising a pair of concentric feeder lines eachline having an inner and an outer conductor, a first doublet having alength equal to half the length of the communication wave conductivelycoupled to the ends of said inner conductors, second and third doubletsof similar lengths in a plane parallel to the plane in which said firstdoublet lies conductively coupled one to one of said outer conductorsand the other to the other of said outer conductors, said parallelplanes being spaced one-half wavelength apart, said outer conductorsextending beyond said ends of said inner conductors for at least halfthe length of the communication wave, and fourth and fifth halfwavelength doublets lying in another parallel plane oppositely disposedto the plane of said second and third doublets with respect to the planeof said first doublet, said fourth doublet being conductively coupled tothe extension of one of said outer conductors and said fifth doubletbeing coupled to the extension of said other outer conductor, and

means for energizing said inner conductors out of phase with respect toeach other.

21. A system in accordance with claim 20, characterized in this thatsaid first doublet is energized from its ends, while said other doubletsare connected to said outer conductors at points intermediate theirends.

22. An antenna system comprising a pair of concentric feeder lines eachline having an inner and an outer conductor, a first doublet having alength equal to half the length of the com munication wave conductivelycoupled to the ends of said inner conductors, second and third dou-'blets of similar lengths in a plane parallel to the plane in which saidfirst doublet lies conductively coupled one to one of said outerconductors and the other to the other of said outer conductors, saidparallel planes being spaced one-half wavelength apart, said outerconductors extending beyond said ends of said inner conductors for atleast half the length of the communication wave, and fourth and fifthhalf wavelength doublets lying in another parallel plane oppositelydisposed to the plane of said second and third doublets with respect tothe plane of said first doublet, said fourth doublet being conductivelycoupled to the extension of one of said outer conductors and said fifthdoublet being coupled to the extension of said outer conductor, andmeans for energizing said inner conductors out of phase with respect toeach other, said fourth doublet being coupled to the same outerconductor as said second doublet, and said fifth doublet being coupledto the same outer conductor as said third doublet, said fourth andsecond doublets being parallel, and said fifth and third doublets beingparallel.

;23. An antenna system in accordance with claim 16, characterized inthis that said aerial elements are each a half wavelength long and saidplanes are spaced a half wavelength apart,- said second and thirddoublets being coupled to said outer conductors intermediate the ends ofsaid, doublets.

24. In combination, a plurality of pairs of vertical parallel feederlines in the form of a cage, aerial elements coupled to said lines, andmeans for energizing each of said pairs such'that corre spondinglylocated points on the feeders of each pair have opposite instantaneouspolarities, said means comprising a U-shaped conductor a half wavelengthlong connecting together the bottom ends of each pair of feeder lines,and a single feeder line connecting one bottom end of one feeder of eachpair to high frequency apparatus.

25. A system in accordance with claim '24, characterized in this thatthe impedance of the single feeder line associated with the U-shapedconductor is equal to half the surge impedance of each vertical feederline of its pair.

an angle of 60 with respect to each other, said conductors beingPhysically separated from each other and in the form of a V, whereby oneend of one conductor is more closely located to one end of the otherconductor than the other ends of said conductors are to each other, eachof said conductors being substantially one-half the length of thecommunication wave, and means for exciting said conductors such thattheir adjacent ends have opposite instantaneous polarities.

27. An antenna system comprising two conductors in the same plane anddisposed substantially at an angle of 60 with respect to each other,each of said conductors being one-half the length of the communicationwave, the centers of said conductors being spaced apart by a distanceapproximately equal to one-quarter of the length of the communicationwave, and means for exciting said conductors to have oppositeinstantaneous polarities at correspondingly located points.

28. An antenna system comprising three spaced aerial elements in' thesame plane forming an equilateral triangle, each of said elements havinga length equal toone-half the length of the communication wave, a loophaving an overall length of one-half wavelength connecting together theend of one element with the adjacent end of another element, similarloops coupling together the other adjacent ends of said elements, asimilar equilateral triangle of elements in a parallel plane andsimilarly positioned, a pair of feeders connecting each loop of onetriangle with the correspondingly located loop of the other triangle,said equilateral triangles of radiating elements being spaced apartsubstantially by the length of the communication wave, and highfrequency apparatus coupled directly to only one of said loops of one ofsaid triangles for energizing all aerial elements of both triangleswhereby adjacent ends of said aerial elements have oppositeinstantaneous polarities, similarly located ends of said elements indiiferent planes having polarities of the same sign.

29. An antenna system comprising three spaced aerial elements in thesame plane forming an open-ended equilateral triangle, each of saidelements having a length equal to one-half the length of thecommunication wave, another similar equilateral triangle similarlylocated in a parallel plane and spaced from said first plane by adistance equal to half the length of the communcation wave,- means forenergizing the aerial elements in one plane in such manner that theadjacent ends of said elements in said one plane have oppositeinstantaneous polarities, a pair of feeders connecting the adjacent endsof the elements in said one plane'to the similarly positioned adjacentends of the elements in the other plane such that said elements in thelast plane also have their adjacent ends at opposite instantaneouspolarities.

30. An antenna system comprising three spaced aerial elements in thesame plane forming an equilateral triangle, each of said elements having a length equal to one-half the length of the communication wave, thecenters of adjacent aerial elements being spaced apart by a distanceapproximately equal to one-quarter of the length of the communicationwave, and means for exciting said elements such that adjacent ends ofthe elements have opposite instantaneous polarities.

tric feeder line having inner and outer conductors,

31. An antenna system comprising a concenan aerial element conductivelycoupled to said inner conductor, another aerial element in a planeparallel to the plane of said first element conductively coupled to saidouter conductor, said planes being spaced a predetermined distanceapart, means for supplying energy to said inner conductor for directlyexciting said first aerial element, whereby said other aerial element isexcited from said outer conductor.

32. An antenna system comprising a pair of concentric feeder lines eachline having an inner and an outer conductor, a first doublet having alength equal to half the length of the communication wave conductivelycoupled at its ends to the ends of said inner conductors, second andthird doublets each of similar length in a plane parallel to the planein which said first doublet lies conductively coupled one to one of saidouter conductors and the other to the otherof said outer conductors,said parallel planes being spaced onehalf wavelength apart, said outerconductors extending beyond said ends of said inner conductors for atleast half the length of the communication wave, and fourth and fifthhalf wavelength doublets lying in another parallel plane oppositelydisposed to the plane of said second and third doublets with respect tothe plane of said first doublet, said fourth doublet being conductivelycoupled to the extension of one of said outer conductors and said fifthdoublet being coupled to the extension of said, other outer conductor,and

. means for energizing said inner conductors out of phase withrespect toeach other.

33.v An antenna system in accordance with claim 16, characterized inthis that said aerial elements are each a half wavelength long and saidplanes are spaced a half wavelength apart, said second, third, fourthand fifth doublets being coupled to said outer conductors intermediatethe ends of said doublets.

34. An antenna system comprising three spaced aerial elements in thesame horizontal plane forming a central equilateral triangle, a pair ofvertical feeders for each of said aerial elements, said aerial elementsbeing connected to said feeders from the ends of the elements, upper andlower equilateral triangles of aerial elements located on opposite sidesof said central triangle of aerial elements, all of said triangles ofaerial elements being in horizontal planes, said planes being separatedfrom one another by a distance substantially equal to half the length ofthe communication wave, each of the aerial elements in said trianglesbeing electrically equal to onehalf. the length of the communicationwave, said points intermediate the ends of the elements,

whereby adjacent ends of aerial elements in the same triangle haveopposite instantaneous polarities.

35. An antennasystem comprising three spaced aerial elements in the samehorizontal plane forming a central equilateral triangle, a pair ofvertical feeders for each of said aerial elements, said aerial elementsbeing connected to said feeders from the ends of the elements, upper andlower equilateral triangles of aerial elements located on opposite sidesof said central "triangle of aerial elements, all of said triangles ofaerial elements being in horizontal planes, said planes being separatedfrom one another by a distance substantially equal to half the length ofthe communication wave, each of the aerial elements in said trianglesbeing electrically equal to one-half the length of the communicationwave, said aerial elements in the upper and lower triangles beingenergized by said vertical feeders at spaced points intermediate theends of the elements, whereby adjacent ends of aerial elements in thesame triangle have opposite instantaneous polarities, said aerialelements in the upper triangle each having a parallel aerial element inthe lower triangle, located in a corresponding position and fed by thesame feeders, said aerial elements in said central triangle each beingpositionedat an angle with respect to the aerial elements in the upperand lower triangles which are connected to the same feeders.

36. An antenna system comprising a plurality of equilateral triangles ofaerial elements located in parallel planes at different levels, andmeans for exciting the aerial elements of each triangle such thatadjacent ends of the elements have opposite instantaneous polarities andthe currents in the aerial elements'of adjacent triangles are in thesame direction.

3'7. An antenna system in accordance with claim 35, characterized inthis that said feeders comprise concentric lines upon which the aerialelements of said triangles are mounted, said lower triangle of aerialelements being positioned onequarter of a wavelength above a surface ofrelatively fixed radio frequency potential.

38. An antenna system comprising three equilateral triangular units ofaerial elements located in parallel planes at different levels,substantially one-half wavelength apart, each of said aerial elementsbeing equal electrically to half the length of the communication wave,and means for exciting the aerial elements of each triangle such thatadjacent ends of the elements have opposite instantaneous polarities andthe currents in the aerial elements of adjacent triangles are in thesame direction.

39. An antenna system comprising three equilateral triangular units ofaerial elements located in parallel planes at different levelssubstantially one-half wavelength apart, each of said aerial elementsbeing equal electrically to half the length of the communication wave,three pairs of vertical feeders for said aerial elements, said elementsbeing mounted on said feeders and electrically coupled thereto at spacedpoints intermediate the ends of the elements, such that the adjacentends of the aerial elements of each triangle are excited to haveopposite instantaneous polarities and the currents in the aerialelements of adjacent triangles are in the same direction.

40. An antenna system comprising three equilateral triangular units ofaerial elements located,

length of the communication wave, three pairs of vertical feeders forsaid aerial elements, said elements being mounted on said feeders andelectrically coupled thereto at spaced points intermediate the ends ofthe elements, such that the adjacent ends of the aerial elements of eachtriangle are excited to have opposite instantaneous polarities and thecurrents in the aerial elements .of adjacent triangles are in the samedirection,

, thickness for changing the impedance of the feeders to more closelymatch the impedance of the aerial elements.-

42. An antenna system comprising a plurality of equilateral triangles ofaerial elements located in parallel planes at different levels, threepairs of vertical feeders for said aerial elements, said feeders beingin the form of a cage, said elements being mounted on said feeders andelectrically coupled thereto at spaced points intermediate the ends ofthe, elements, metallic braces connecting the feeders together, saidbraces being in effect inductances which electrically are shunted acrosssaid aerial elements, said aerial elements being each physically longerthan, but electrically equal to one-half the length of the communicationwave.

43. In combination, a transmission line feeder, a plurality of aerialelements coupled to said feeder at points spaced along the length ofsaid feeder, the dimensions of said feeder decreasing between successiveaerial elements for increasing the impedance of said feeder.

44. In an antenna system, a concentric transmission line having an innerand an outer conductor, a first aerial element coupled to said outerconductor,-a second aerial element'coupled to said inner conductor, saidaerial elements being in parallel planes spaced substantially onehalfwavelength apart, said inner conductor having an abrupt change indimensions between said aerial elements at a point substantiallyonequarter of a wavelength from the point of connection to said secondaerial element, whereby the NILS E. LINDENBLAD.

-ductors is increased.

